1. Field of the Invention
This invention relates to clock frequencies in a computer system and more particularly to microprocessor frequency detection and selection.
2. Description of the Related Art
Modern day computer systems, particularly personal computer systems, include a system unit having a system processor or microprocessor with associated volatile and non-volatile memory, a display monitor, a keyboard, one or more floppy diskette drives, a hard disk storage device and an optional printer. One of the distinguishing characteristics of these systems is the use of a system board or motherboard to electrically connect these components together. A personal computer system may also include one or a plurality of I/O devices (i.e. peripheral devices) which are coupled to the system processor and which perform specialized functions.
Computer systems operate under the control of one or more "clocks" or signal lines carrying a signal of a predetermined frequency and duty cycle. The clock signal is provided to various components in the computer system and these components typically carry out some operation or set of operations during one or more "clock cycles" or cycles of the signal. The coordination of all the processes between a microprocessor and main memory is carried out using the clock signal from the clock generator. Without this signal, complete chaos would arise, and correct data transfer would be impossible. However, the clock signals lead to correct execution, and give the individual circuits enough time to fulfill their tasks.
Of course, the various components of the computer system must be designed to match the clock speed or frequency. The computer system must be designed to provide a clock signal of the appropriate clock speed to circuits used in the computer system. This creates a special problem in multiple microprocessor computer systems where it is desired to operate all components under the control of a single clock and, for example, only one of the processor modules is upgraded with a higher speed microprocessor. Synchronization between microprocessors is a continuing critical issue in a very wide variety of multiprocessor systems.
Current methods of producing microprocessors includes fabricating and assembling the microprocessor and then testing for its maximum allowable operating clock speed. After testing the microprocessor, it is visibly labeled with a part number and rated clock frequency and then shipped to the end users or customers. The microprocessors are labeled manually and there is no automatic or electronic process for a computer system to know what the maximum rated clock frequency is for that installed microprocessor. Jumpers must be manually set within the computer system when installing the microprocessor. Also, in multiprocessor environments where microprocessors of the same family could be installed in the same system bus, each with different maximum rated frequencies, a problem of synchronization of the multiple microprocessors to the same clock frequency (i.e. usually the lowest common frequency) may occur. Therefore, a system is needed to automatically detect and select the common operating external/internal clock frequencies in a multiprocessor system when the microprocessors are installed.